The invention pertains generally to pyrotechnic compositions and particularly to metal-cutting pyrotechnic compositions.
Pyrotechnic compositions are placed in metal cutting torches and are then used in salvaging and demilitarizing ordnance. The object is to develop one or more exothermic reactions among the ingredients in order to melt an area on a work piece and preferably initiate an exothermic combustion of a metallic component of the work piece.
It is necessary for a composition to quickly generate a large amount of heat per unit volume of composition without generating an appreciable amount of gas. These requirements are especially critical in the demilitarizing ordnance. If a warhead casing is not breached before the charge begins to react, a detonation often results. If a large volume of gas is generated, the torch can break contact with the work piece, thereby reducing the chances of breaching the casing before initiating the charge reaction. Further, gas generation, as an incident of oxygen reactions, absorbs the heat of reaction and removes it from the reaction system.
Cutting torches are often stored for long periods of time. Consequently, pyrotechnic compositions must be stable; so that, the cutting torch does not detonate or burn too slowly and has a predictable burning behavior. Also it is advantageous that the composition is hard to ignite for safety reasons.
Many exothermic reactions have been utilized in formulating pyrotechnic compositions, including the reactions of oxygen with a metal, fluorine and other halogens with a metal, aluminum with iron oxide, and sulfur with iron. For example, U.S. Pat. No. 3,565,706 by H. R. Waite, issued on Feb. 23, 1971, utilizes the exothermic reaction of metals with oxygen or fluorine. The composition comprises a metal fuel selected from the group consisting of IIIb, IVb, Vb metals and an oxidizing binder comprising at least 50% of a fluorohydrocarbon. This composition is used primarily in incendiary bombs. As such, gas generation and the expense of the metal fuel are not as critical as they are in compounding metal cutting pyrotechnic compositions. A mixture of iron and sulfur in U.S. Pat. No. 1,035,202 by Albert Lang, issued on Aug. 13, 1912, is disclosed as a pyrotechnic composition but the composition is not suitable for most metal cutting applications, especially ordnance demilitarization because of a lack of mechanical strength in a pellet or disc of the composition, the relatively low heat production per unit volume of composition, and the large amount of obnoxious sulfur oxide fumes.
The advantages of a fluorocarbon polymeric material as a binder and source of fluorine for oxidation, as well as, the large amount of heat released upon oxidation of magnesium, are disclosed in U.S. Pat. No. 4,013,491 by Graham C. Shaw and Russell Reed, Jr., issued on Mar. 22, 1977. The incendiary composition consists essentially of particulate magnesium and a mono- or di-fluoroalkyl phosphate ester. The disadvantages of this composition are a short pot life, aging problems, and poor homogeneity. In U.S. Pat. No. 3,890,174, compositions comprising, for example aluminum, copper, ferric oxide (Fe.sub.2 O.sub.3) and Teflon are disclosed. These compositions, while liberating a large amount of heat have the disadvantage of generating gas which causes an increase in pressure.
Some pyrotechnic compositions include an oxidizer in addition to air in order to increase the rate of the oxidation reaction. In U.S. Pat. No. 3,890,174, e.g., the fluorocarbon is used as an oxidizer.
A composition which has been considered for pyrotechnic uses comprises gypsum (CaSO.sub.4.2H.sub.2 O), aluminum, and water. But due to its unreliability, sometimes burning too slowly and other times detonating, this composition has not been adopted. The advantages of this composition are several: inexpensive materials, simple processing, and extremely high heats of reaction. If the reliability of this composition could be improved or a composition with similar but more reliable materials could be formulated, the composition would be an excellent pyrotechnic composition for metal-cutting applications, such as ordnance demilitarization.